Explanation:
Light is more complicated than we thought.
When astronomers measure
light, they are usually concerned with its direction, energy, and
spin polarization (sometimes).
Recently, however, it has been more broadly
realized that photons can also have
orbital angular momentum (OAM),
an attribute classically analogous to the
Earth orbiting the Sun as well as spinning on its axis.
Pictured above, the wave-front of a photon with
OAM is shown to be twisted, in contrast to the flat plane of zero OAM light.
Light with OAM might be used to increase the
information content of communication or to discern
specific types of astronomical sources.
Passing through a common lens, light without OAM focuses to a point,
whereas light with OAM focuses to a ring.
Most light bouncing around the cosmos,
however, is expected to have so little (or zero)
OAM that the created ring is too small to measure.
Even given other promising methods for measurement, exploiting OAM for
astronomical discovery might be as much an issue of
observational practicality as theoretical possibility.